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Czerwinski RM, Nieznanski K, Sochanowicz B, Staron K. PKA controls a level of topoisomerase I mRNA in mouse L5178Y lymphoma cells treated with db-cAMP. Mol Biol Rep 1994; 19:93-7. [PMID: 8072495 DOI: 10.1007/bf00997153] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The level of topoisomerase I mRNA was measured in cells of two mouse lymphoma (LY) sublines treated with db-cAMP. A transient increase of the level was observed to be of about 60% of the basic level and to have maximum after the 3 h treatment of LY-S cells. The increase in LY-R subline was two-fold lower. The activity of PKA in a cytosol fraction of LY-S cells was 1.75 times higher than that in LY-R cells. The activity of PKA in membranes and nuclear fraction did not differ significantly in both cell types. When the activity of PKA in LY-S cells was inhibited with H8, no increase of the level of topoisomerase I mRNA was observed upon db-cAMP treatment of cells. We suggest that the activity of PKA in the cytosol controls the expression of topoisomerase I gene in LY cells at high concentration of cAMP.
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2
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Nokta MA, Pollard RB. Human immunodeficiency virus replication: modulation by cellular levels of cAMP. AIDS Res Hum Retroviruses 1992; 8:1255-61. [PMID: 1381600 DOI: 10.1089/aid.1992.8.1255] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
HIV infection is associated with qualitative and functional immune deficiencies. It has been shown that the in vitro infection of CD4+ cells with HIV was associated with sustained elevation of cAMP and cGMP. In the present report the role of cAMP on HIV replication in MT-4 cells was investigated. The MT-4 cells were infected with HIV (strain 3b), in the presence or absence of agents that increase intracellular levels of cAMP, through different mechanisms. At selected times postinfection, HIV replication was measured by reverse transcriptase activity or HIV P24Ag in culture supernatants. Forskolin (FK, an activator of adenylate cyclase 1-100 microM), Isobutyl-methylxanthine (IBMX, a phosphodiesterase inhibitor, which indirectly increases intracellular levels of cAMP, 30-100 microM) and dibutyryl (db) cAMP (0.1-10 microM) enhanced HIV replication, in a dose-dependent manner. FK, IBMX, and db cAMP enhanced HIV replication by 2- to 10-fold, 4- to 7-fold, and 2- to 6-fold, respectively. Intracellular levels of cAMP were measured by radioimmunoassay and were also enhanced. Since cAMP exerts its catalytic effects through activation of protein kinase (PK) A the effect of H-8 (a specific inhibitor of the cAMP dependent PK A) on HIV replication was simultaneously examined. The H8 at doses of 0.1 to 10 microns inhibited HIV replication by 25 to 99.9%. Moreover H9 inhibited HIV replication in peripheral blood mononuclear cells by more than 90%. The replication of HIV appears to be a cAMP-dependent event, and PK A could possibly be a target for the development of anti-HIV therapies.
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Affiliation(s)
- M A Nokta
- Department of Internal Medicine, University of Texas Medical Branch, Galveston 77550
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3
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Nokta M, Pollard R. Human immunodeficiency virus infection: association with altered intracellular levels of cAMP and cGMP in MT-4 cells. Virology 1991; 181:211-7. [PMID: 1704657 DOI: 10.1016/0042-6822(91)90486-u] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
T-cells from human immunodeficiency virus (HIV)-infected patients are characterized by a number of qualitative deficiencies including defective T-cell activation. The latter has previously been shown to be normally regulated by cAMP. In this study the patterns of cAMP and cGMP induction in MT-4 cells following HIV infection were investigated. The MT-4 cells were infected with HIV (strain IIIb) and at selected times postinfection (p.i.), culture supernatants were tested for HIV replication by reverse transcriptase activity or HIV P24 Ag. The cells were also examined for their intracellular levels of cAMP and cGMP by radioimmunoassay. HIV infection was associated with an increase in intracellular levels of cAMP and cGMP. The cAMP was increased 40-fold by Day 8 and cGMP 4-fold by Day 4 Pl. The increase in intracellular levels of the cyclic nucleotides (CN) were virus specific, dependent on virus dosage, genetically conserved among the two fresh patient isolates tested, and were abolished by uv inactivation. An increase in cAMP and cGMP was also observed in other cell lines infected with HIV. The sustained elevation in CN level observed could certainly influence cell activation and HIV replication and may potentially have clinical relevance.
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Affiliation(s)
- M Nokta
- Department of Internal Medicine, University of Texas Medical Branch, Galveston 77550
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4
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Collins S, Altschmied J, Herbsman O, Caron M, Mellon P, Lefkowitz R. A cAMP response element in the beta 2-adrenergic receptor gene confers transcriptional autoregulation by cAMP. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(17)30662-2] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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5
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Brown NA, Stofko RE, Uhler MD. Induction of alkaline phosphatase in mouse L cells by overexpression of the catalytic subunit of cAMP-dependent protein kinase. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)38283-3] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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6
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Browne CL, Bower WA, Palazzo RE, Rebhun LI. Inhibition of mitosis in fertilized sea urchin eggs by inhibition of the cyclic AMP-dependent protein kinase. Exp Cell Res 1990; 188:122-8. [PMID: 2328770 DOI: 10.1016/0014-4827(90)90286-j] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Inhibition of cAMP-dependent protein kinase activity by microinjection of a specific physiologic protein inhibitor into sea urchin eggs inhibits the first cleavage after fertilization. Inhibition apparently occurs at some time prior to or during formation of the mitotic spindle. Measurement of the total protein kinase activity of sea urchin egg homogenates after fertilization showed that cAMP-dependent phosphorylation increases after fertilization and then declines prior to or at the time of the first cleavage. It is concluded that a cAMP-dependent phosphorylation plays a significant role in events leading to regulation of mitotic spindle assembly.
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Affiliation(s)
- C L Browne
- Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109
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7
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Cyclic Nucleotides. Mol Endocrinol 1989. [DOI: 10.1016/b978-0-12-111230-1.50011-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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8
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Requirements of both glucocorticoids and glucagon as co-inducers for activation of transcription of the serine dehydratase gene in cultured rat hepatocytes. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)68103-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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9
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Kohli KK, Obuch A, Stellwagen RH. Protection of tyrosine aminotransferase against proteolytic digestion by nucleotide derivatives. BIOCHIMICA ET BIOPHYSICA ACTA 1988; 956:77-84. [PMID: 2900654 DOI: 10.1016/0167-4838(88)90300-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The abilities of several nucleotides to protect tyrosine aminotransferase (L-tyrosine: 2-oxoglutarate aminotransferase, EC 2.6.1.5) against proteolytic inactivation in vitro have been examined as part of an ongoing investigation of the role of cyclic GMP in the intracellular degradation of the hepatic enzyme. Although neither cyclic GMP nor cyclic AMP was found to exert such a protective effect, certain nucleotide analogs were observed to inhibit the inactivation of tyrosine aminotransferase by trypsin and chymotrypsin. The nucleotides which conferred the strongest protection were the dibutyryl derivatives of cyclic GMP and cyclic AMP. This phenomenon appears to require a purine nucleotide with hydrophobic substituent(s), while the cyclic phosphate is not essential. The nucleotides probably act by direct interaction with tyrosine aminotransferase as indicated by changes in kinetic properties and heat stability of the enzyme and by their failure to inhibit trypsin when other protein substrates, including another aminotransferase, were used. Dibutyryl cyclic AMP was shown to block the appearance of a characteristic 43 kDa tryptic cleavage product of tyrosine aminotransferase but not the conversion of the native 54 kDa form to a size of 50 kDa. Arguments are presented against the involvement of the protective effect in the actions of dibutyryl cyclic nucleotides on tyrosine aminotransferase in cells.
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Affiliation(s)
- K K Kohli
- Department of Biochemistry, University of Southern California School of Medicine, Los Angeles 90033
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10
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Sikorska M, Whitfield JF, Walker PR. The regulatory and catalytic subunits of cAMP-dependent protein kinases are associated with transcriptionally active chromatin during changes in gene expression. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)69167-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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11
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Kitagawa Y. Hormonal regulation of carbamoyl-phosphate synthetase I synthesis in primary cultured hepatocytes and Reuber hepatoma H-35. Defective regulation in hepatoma cells. EUROPEAN JOURNAL OF BIOCHEMISTRY 1987; 167:19-25. [PMID: 3040399 DOI: 10.1111/j.1432-1033.1987.tb13299.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Regulation of carbamoyl-phosphate synthetase I (CPS) synthesis by various hormones was compared in primary cultured hepatocytes from adult rat and in Reuber hepatoma H-35 by pulse labeling of the cells with [35S]methionine. CPS synthesis in hepatocytes was stimulated 8-fold and 5-fold by dexamethasone and glucagon respectively. CPS synthesis in hepatocytes was synergically (about 50-fold) stimulated by a combination of dexamethasone and glucagon. Less synergic stimulation was observed by combining dexamethasone with N6, O2'-dibutyryladenosine 3',5'-monophosphate (dibutyryl-cAMP) or with isoproterenol. The basal level of CPS synthesis in hepatoma cells was higher than that in hepatocytes. CPS synthesis in hepatoma cells was stimulated by dexamethasone and dibutyryl-cAMP but the extent was only 3-fold and 1.8-fold respectively. The synergic effect of combination of dexamethasone and dibutyryl-cAMP was not observed in hepatoma cells. Neither glucagon nor isoproterenol exhibited an appreciable effect on CPS synthesis in hepatoma cells. Insulin and epinephrine suppressed CPS synthesis both in hepatocytes and hepatoma cells. The effect of epinephrine was indicated to be through alpha-adrenergic receptors. The effects of insulin and epinephrine were additive on CPS synthesis both in hepatocytes and hepatoma cells.
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12
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Schmid E, Schmid W, Jantzen M, Mayer D, Jastorff B, Schütz G. Transcription activation of the tyrosine aminotransferase gene by glucocorticoids and cAMP in primary hepatocytes. EUROPEAN JOURNAL OF BIOCHEMISTRY 1987; 165:499-506. [PMID: 2885194 DOI: 10.1111/j.1432-1033.1987.tb11467.x] [Citation(s) in RCA: 107] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The expression of the tyrosine aminotransferase (TAT) gene of the rat was analyzed in primary hepatocytes. The TAT gene remains active in primary cultured cells at a level similar to that in liver cells. Expression can be induced by glucocorticoids and cAMP, glucocorticoids lead to a 8-10-fold increase in TAT mRNA level, cAMP to a 20-30-fold increase. The elevation of the TAT mRNA is preceeded by a rise in the relative rate of transcription of the gene. Surprisingly transcription of the albumin gene, which steadily declines with the age of the culture, can also strongly be stimulated by glucocorticoids in primary hepatocytes. cAMP antagonists, which act as competitive inhibitors of the cAMP-dependent protein kinase, prevent induction of transcription of the tyrosine aminotransferase gene by cAMP suggesting that the effect of cAMP on expression of the tyrosine aminotransferase gene is mediated by a cAMP-dependent protein kinase. The cAMP antagonist does not interfere with induction by glucocorticoids which suggests that phosphorylation of the glucocorticoid receptor by the cAMP-dependent protein kinase is not required for its function. We thus conclude that the two inducers affect transcription by independent mechanisms.
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Jungmann RA, Constantinou AI, Squinto SP, Kwast-Welfeld J, Schweppe JS. Regulation of lactate dehydrogenase gene expression by cAMP-dependent protein kinase subunits. Ann N Y Acad Sci 1986; 478:147-61. [PMID: 3026220 DOI: 10.1111/j.1749-6632.1986.tb15528.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The studies described in this report suggest a rather complex, albeit incomplete, sequence of molecular events that we believe form part of the cascade of reactions through which a series of hormones, via cAMP, regulates the expression of specific gene products. The majority of our own studies relate to cAMP-mediated induction of LDH. Some, if not all, of the molecular steps discussed in this paper may ultimately be recognized as part of a universal mechanism by which cAMP controls gene expression in higher eukaryotes. The idea of a functional role for cAMP-dependent protein kinase subunits in cAMP-mediated gene control has already had experimental support, but our identification of the regulatory subunit RII as a topoisomerase now more firmly points to a complex function for the kinase in regulating gene function at the DNA level. We look forward to the elucidation of the function of those nuclear proteins that serve as substrate for the catalytic subunit of cAMP-dependent protein kinase. Further studies related to the molecular interaction of RII with chromosomal DNA should be a fruitful area for future research.
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14
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Vaulont S, Munnich A, Decaux JF, Kahn A. Transcriptional and post-transcriptional regulation of L-type pyruvate kinase gene expression in rat liver. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(19)57443-9] [Citation(s) in RCA: 98] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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15
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Woffendin C, Chambers TC, Schaller KL, Leichtling BH, Rickenberg HV. Translocation of cAMP-dependent protein kinase to the nucleus during development of Dictyostelium discoideum. Dev Biol 1986; 115:1-8. [PMID: 3009250 DOI: 10.1016/0012-1606(86)90221-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The distribution of the catalytic and regulatory subunits of the cAMP-dependent protein kinase between cytoplasm and nucleus was determined during the development of Dictyostelium discoideum. In vegetative amoebae approximately 2% of the subunits were in the nucleus. During development there was an approximately 5-fold increase in total soluble cAMP-dependent protein kinase and a 15- to 30-fold increase of enzyme in the nuclear fraction. There was a reverse translocation from nucleus to cytoplasm, when Tipped Aggregates were disrupted and the resultant amoebae incubated in single-cell suspension. The addition of cAMP to these single-cell suspensions brought about the reentry of the subunits into the nucleus. The findings are discussed in relation to the potential role of the cAMP-dependent protein kinase in the regulation of mRNA and protein synthesis.
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16
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Beebe SJ, Corbin JD. 3 Cyclic Nucleotide-Dependent Protein Kinases. ACTA ACUST UNITED AC 1986. [DOI: 10.1016/s1874-6047(08)60428-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
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17
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Waterman M, Murdoch GH, Evans RM, Rosenfeld MG. Cyclic AMP regulation of eukaryotic gene transcription by two discrete molecular mechanisms. Science 1985; 229:267-9. [PMID: 2990047 DOI: 10.1126/science.2990047] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In experiments designed to study the mechanism by which peptide hormones binding to their plasma membrane receptors stimulate the expression of specific genes, the transcription of two neuroendocrine genes, prolactin and growth hormone, was analyzed in a rat pituitary cell line. The results showed that cyclic adenosine monophosphate (cyclic AMP) stimulates the transcription of discrete subsets of eukaryotic genes by at least two independent molecular mechanisms. Cyclic AMP stimulated growth hormone gene transcription and phosphorylation of a 19,000-dalton nuclear protein; this appears to reflect direct nuclear actions of the cyclic AMP-dependent protein kinase. In contrast, the stimulation by cyclic AMP of prolactin gene transcription appears to reflect activation of a discrete calcium-dependent event.
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18
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Driscoll DM, Schreiber JR, Schmit VM, Getz GS. Regulation of apolipoprotein E synthesis in rat ovarian granulosa cells. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(17)39453-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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19
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de Gunzburg J. [Mode of action of cyclic amp in prokaryotes and eukaryotes, CAP and cAMP-dependent protein kinases]. Biochimie 1985; 67:563-82. [PMID: 2413906 DOI: 10.1016/s0300-9084(85)80196-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
cAMP is an ubiquitous compound which is involved in the regulation of many biological processes. In bacteria such as E. coli, cAMP mediates the activation of catabolic operons via the CAP protein. The CAP-cAMP complex, whose tridimensional structure has recently been established, binds to the promoter regions of catabolic operons at a specific site, and activates their transcription by inducing RNA polymerase to bind and initiate transcription at the correct site. Various phenomenons including protein-protein interactions or CAP-induced DNA bending or kinking could be involved in the process of forming the open transcription complex. In eukaryotes, cAMP activates cAMP dependent protein kinases which covalently modify proteins by phosphorylation on serine or threonine residues. The catalytically inactive holoenzyme is generally a tetramer containing two regulatory subunits, each capable of binding two molecules of cAMP, and two catalytic subunits. In mammalian cells, two types of cAMP dependent protein kinases (I and II) can be distinguished on the basis of their regulatory subunits; their relative proportion varies from tissue to tissue. Binding of cAMP to the regulatory subunits induces the dissociation of the holoenzyme and releases the free and active catalytic subunits. Phosphorylation of proteins occurs at sequences containing two basic residues in the vicinity of the phosphorylated serine or threonine. A heat-stable protein, present in most eukaryotic cells, specifically interacts with the catalytic subunit and inhibits its activity. The amino-acid sequence of cAMP dependent protein kinases has recently been determined. It is interesting to note that the domains responsible for cAMP binding by the regulatory subunits of mammalian cAMP dependent protein kinases and CAP share important sequence homologies. The same phenomenon is observed concerning the domain responsible for ATP binding to the catalytic subunit of cAMP dependent protein kinases and that of tyrosine-specific protein kinases from oncoviruses. Other eukaryotic proteins such as S-adenosyl-L-homocysteine (SAH) hydrolase are also capable of binding cAMP. The latter is involved in the regulation of S-adenosyl-L-methionine dependent methylations, and its activity could be affected by cAMP. Besides its role as an effector of enzymatic activity via phosphorylation, such as in the regulation of glycogen metabolism, cAMP has recently been shown to activate the transcription of a number of eukaryotic genes. This process probably also involves protein phosphorylation, but its precise mechanism remains to be understood.
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Schwartz DA, Rubin CS. Identification and differential expression of two forms of regulatory subunits (RII) of cAMP-dependent protein kinase II in Friend erythroleukemic cells. Differentiation and 8-bromo-cAMP elicit a large and selective increase in the rate of biosynthesis of only one type of RII. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)88970-0] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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21
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Harper JF, Haddox MK, Johanson RA, Hanley RM, Steiner AL. Compartmentation of second messenger action: immunocytochemical and biochemical evidence. VITAMINS AND HORMONES 1985; 42:197-252. [PMID: 3006347 DOI: 10.1016/s0083-6729(08)60063-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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22
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Vaulont S, Munnich A, Marie J, Reach G, Pichard AL, Simon MP, Besmond C, Barbry P, Kahn A. Cyclic AMP as a transcriptional inhibitor of upper eukaryotic gene transcription. Biochem Biophys Res Commun 1984; 125:135-41. [PMID: 6095835 DOI: 10.1016/s0006-291x(84)80345-9] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Recently, glucagon and its second messenger, cyclic AMP, have been shown to stimulate the transcription rate of several upper eukaryotic genes (1-5). We show here that glucagon can also block gene transcription. Both glucagon and cyclic AMP were found to inhibit the transcription of the genes encoding three liver glycolytic enzymes, including L-type pyruvate kinase and aldolase B. Thus, cyclic AMP proves to be not only an activator but also an inhibitor of gene transcription in eukaryotes.
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McElligott MA, Dice JF. Microinjection of cultured cells using red-cell-mediated fusion and osmotic lysis of pinosomes: a review of methods and applications. Biosci Rep 1984; 4:451-66. [PMID: 6380609 DOI: 10.1007/bf01122221] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Proteins and other macromolecules can be injected into cultured cells by several different methods. Here we review the strengths and limitations of two of these methods, red-cell-mediated microinjection and osmotic lysis of pinosomes, and indicate how they may be successfully applied to the study of cultured cells.
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Abstract
The discovery of a role for the cytoskeleton in the responses to ACTH and cyclic AMP was somewhat unexpected - at least this was the case 9 years ago (1). In fact, many endocrinologists are forced to confess that they were innocent of any understanding of the cytoskeleton and were not even aware that all mammalian cells possess microfilaments and microtubules. A new generation of endocrinologists has arrived on the scene who have been brought up with the cytoskeleton so that we can expect to see considerable progress during the coming decade in our understanding of the role of the cytoskeleton in endocrine cells.
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